Heretofore most petroleum coke had little commercial value because of an excessive sulfur content, which made it unacceptable for electrode production and undesirable for use as a fuel. At present the trend is to accept only those cokes having a sulfur content of 1.2 percent or less. Therefore, most petroleum cokes available today cannot be processed by normal calcination techniques to produce an acceptable electrode-grade coke.
For years, the major problem with oil refiners in disposing of petroleum has been the sulfur content of their petroleum coke. Refiners have spent large amounts trying to find a practical economical way of removing excess sulfur from their coke in order to make it commercially usable, but they were not successful. While various coke desulfurization methods were proposed, they did not provide adequate incentive for commercial development and did not provide a satisfactory solution to the problem.
Calcining of coke has also been a problem because of high cost. Rotary hearth calciners have been used for this purpose but have been uneconomical due to high capital investment and high operating expenses. The cost of calcining the coke in rotary kilns is increased because of inordinate loss of coke fines.